Hi, I just did these two problems and the domain was the same for both problems, am I overlooking something?

h(x) = 4x/Square Root(x^2 - 16)

and

j(x) = Square Root[4x/(x^2 - 16)]

Maybe she's trying to trick me?

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- January 9th 2007, 03:04 PMleviathanwaveDomains?
Hi, I just did these two problems and the domain was the same for both problems, am I overlooking something?

h(x) = 4x/Square Root(x^2 - 16)

and

j(x) = Square Root[4x/(x^2 - 16)]

Maybe she's trying to trick me? - January 9th 2007, 03:10 PMleviathanwaveOops!
One more quick thing. I didn't quite know how to approach this one:

The function y=k(x) is a polynomial with x-intercepts 1,2,5 and 8. The solution set to k(x) is (1, 2)U(5,8).

Use this information to find the domain of y= Square Root[k(x)] - January 9th 2007, 04:44 PMThePerfectHacker
The denominator cannot be zero. And the radical must be positive. Thus,

Quote:

j(x) = Square Root[4x/(x^2 - 16)]

First thus, .

And,

Both positive or both negative

1)

And,

thus,

Combination of those two leads us to,

2)

thus, .

Combination of those two leads us to,

.

Even though they are different functions they have the same solution set. - January 9th 2007, 06:55 PMtopsquark
Typically if you want a polynomial with specific x-intercepts you can simply write them out term by term:

If you have the intercepts 1, 2, 5, and 8 a polynomial that fits this is:

Now we want the function to have the domain which means that this is the part of the (real) x-axis for which k(x) is positive. So let's graph f(x). (See the attachment below.)

Note that in the graph the set is the region where f(x) is negative. So we need to "flip the function over" to make this the region where the function is positive. This is easy. Just define k(x) to be the negative of f(x):

.

Then has the correct domain.

Note: Technically the domain is . I couldn't think of a way to define a finite polynomial that excludes the end-points of the sets. (Unless I'm missing the obvious.) You might wish to point this out to your teacher.

-Dan